A compression ignition engine may be fitted with an adjustable valve timing system to improve engine efficiency and power. The adjustable valve timing system may be comprised of one or more camshafts, a cam phase actuator, and timing chains that link the one or more camshafts to an engine crankshaft. The cam phase actuator may adjust a position of the one or more camshafts relative to a position of the camshaft, and lobes on the camshaft operate intake and/or exhaust valves of engine cylinders. Manufacturing tolerances may cause errors between a commanded intake and/or exhaust valve opening time and an actual intake and/or exhaust valve opening time between different vehicles. An error in cylinder valve timing may increase engine emissions or reduce engine power. Therefore, it may be desirable to control actual cylinder valve timings to commanded valve timings so that desired engine emissions and performance may be more consistent over a fleet of vehicles.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: adjusting a commanded exhaust valve opening timing via a controller in response to an exhaust valve opening timing determined from a rate of change of pressure in a cylinder of an engine.
By adjusting a commanded exhaust valve opening time responsive to an exhaust valve opening timing determined via a rate of change in cylinder pressure, it may be possible to provide the technical result of improving exhaust valve timing control. Further, by providing more precise exhaust valve timing, control of engine expansion work and engine emissions may be improved. In one example, a rate of change of cylinder pressure during a prescribed crankshaft angle window is a basis for determining exhaust valve opening timing. The commanded exhaust valve timing may be adjusted responsive to the exhaust valve opening timing determined from the rate of change of cylinder pressure during the prescribed crankshaft angle window.
The present description may provide several advantages. For example, the approach may improve exhaust valve timing control. Further, the approach may reduce engine emissions and improve engine fuel economy. Further still, the approach may be suitable for adjusting exhaust valve timing of a cylinder bank in response to output of a single pressure sensor located in one cylinder of a cylinder bank.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.